This invention relates generally to automotive emission control valves and systems, such as exhaust gas recirculation (EGR) valves that are used in exhaust emission control systems of automotive vehicle internal combustion engines. More specifically, the invention relates to an improvement for measuring the gas flow in an emission control valve and/or system.
Commonly owned U.S. Pat. No. 6,116,224 (Cook and Busato) discloses an EGR system comprising an EGR module. One element of that module is a pressure sensor that senses pressure differential across a circular orifice through which exhaust gas flow is constrained to pass when a valve of the module allows flow to the engine intake system.
A circular orifice of given diameter possesses a known relationship between flow through the orifice and pressure drop across the orifice. In other words, flow through the orifice, and hence flow through the module, can be calculated by measurement of pressure drop across the orifice and applying the known flow/pressure drop relationship to the pressure drop measurement. U.S. Pat. No. 6,116,224 shows various embodiments for communicating the pressure drop across the orifice to the pressure sensor.
Actual measurements of flow through such modules at different pressure drops across their orifices have shown a certain amount of scatter relative to a relationship that should theoretically exist for an ideal orifice. It is believed that greater precision in flow control can be obtained if the amount of scatter can be reduced, and it is toward that objective that the present invention is directed.
The invention arises out of several discoveries. A first discovery is that scatter can be reduced by how the sensing port of a pressure sensor is communicated to the gas flow passage that extends through a module. A second discovery is that scatter can be reduced by using a nozzle instead of an orifice. A third discovery results from combining the first two discoveries.
One generic aspect of the invention relates to an internal combustion engine exhaust emission control system comprising a flow path for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine. A valve selectively restricts the flow path. A pressure sensor having a pressure sensing port is communicated via a pressure sensing passage to the flow path. A side wall bounds a portion of the flow path, and the pressure sensing passage comprises a tube having an end portion passing through a through-hole in the side wall of the flow path to dispose an open free end of the tube within the flow path in spaced relation to the side wall.
A further generic aspect relates an internal combustion engine exhaust emission control system comprising a flow path for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine. A valve selectively restricts the flow path. A pressure sensor having a pressure sensing port is communicated via a pressure sensing passage to the flow path. A side wall bounds a portion of the flow path, and the pressure sensing passage comprises a tube having an end portion passing through a through-hole in the side wall of the flow path to communicate an open free end of the tube to the flow path in spaced relation to the side wall. A nozzle is disposed in the flow path opposite the open free end of the tube.